The prior art optical spectrum analyzer indicates the average value of light power existing within a finite slit width, or a finite spectral width.
A spectrograph using a detector array has been urged to display the output from each device as it is, for the following reason. The spectrum of light under measurement is assumed to have an arbitrary shape. The spectral shape does not always have a 1:1 relation to the output from the device array.
Accordingly, it has been difficult to estimate the real spectral shape from the output from the device array.
Furthermore, the wavelength resolution and the range of measured wavelengths are determined by the number of the devices of the array, the pitch, the focal distance of the focusing mirror, and other factor. Trade-offs are made between the wavelength resolution and the range of measured wavelengths. Therefore, if one is improved, then the other is deteriorated. It is impossible to improve both at the same time.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide an optical spectrum analyzer which assumes that light under investigation is an assemblage of monochromatic light rays (light whose spectral linewidth is much narrower than the resolution of the instrument such as laser light) and which can find the center wavelength of the monochromatic light and the total power by performing simple arithmetic operations from the outputs from adjacent devices of a device array.
It is another object of the invention to realize an optical spectrum analyzer capable of measuring ASE noise buried in laser light and of equivalently improving the dynamic range.
It is a further object of the invention to realize a spectrometer apparatus which is applicable to an optical spectrum analyzer and which is provided with a plurality of incident ports, or slits, to extend the range of measured wavelengths while maintaining desired wavelength resolution.